A need for reducing the marking time has recently arisen in the technical field related to marking devices, including laser markers.
In the past, to mark an "ABCDE" marking pattern such as that shown in FIG. 2 using the laser marker shown in FIG. 1, an entire original image 18 was uniformly divided into image segments 19 of a predetermined size, all these image segments 19 were sequentially displayed on the display screen 10 of a liquid-crystal mask 6, and actuators 12 and 16 for switching an image-segment exposure position 17a on a work 17 were driven in controlled fashion every time the display was switched.
In such cases, display switches and actuator drive/control are also performed for image segments 19', which represent only the background outside of the "ABCDE" marking pattern. This means that so-called blank spaces are also marked, and the time for display switches and the like is wasted. The same is true for images such as an image segment 19", where the marking pattern occupies only a small share of the entire image 19".
A first object of the present invention, which was devised in view of this situation, is to reduce the marking time by reducing the number of divisions when an original image is divided into image segments.
In the laser marker shown in FIG. 1, a laser beam ba strikes the display screen 10 of the liquid-crystal mask 6, and the entire display screen 10 is marked by scanning the laser beam, as shown in FIG. 16. Main scanning of the display screen 10 in the X direction is effected by the rotation of a polygonal mirror 3, and sub scanning in the Y direction is effected by the rotation of a scanning mirror 2.
In the past, to continue to perform main scanning once the preceding cycle of main scanning had been completed, it was necessary to vary the rotational speed of the scanning mirror 2 in steps from zero speed and to proceed from an initial sub scanning position Y1 to a next sub scanning position Y2.
Such a stepwise scanning mode does not pose any problems when the polygonal mirror 3 rotates at a low speed and the main scanning is performed at a low speed, but it is impossible to track when the main scanning is performed at a fast speed, and undesirable vibration results.
A second object of the present invention, which was devised in view of this situation, is to reduce the marking time by raising the scanning speed of the display screen of the mask without impairing the tracking properties or bringing about other disadvantages.
When an image such as that shown in FIG. 24 is marked with the aid of the laser marker shown in FIG. 1, then, as described above, an image 33 is divided into the image segments 19 of the predetermined size, these image segments 19 are sequentially displayed on the display screen 10 of a liquid-crystal mask 6, and actuators 12 and 16 for switching an image-segment exposure position 17a on a work 17 are driven in controlled fashion every time the display is switched.
The dimensions of the image 33 and image segments 19 often vary with the type of device and correspond to rectangular shapes with varying longitudinal and transverse dimensions.
In the past, the display switching sequence for image segments 19 was unconditionally defined as a sequence involving a large number of travel cycles in the transverse direction, as shown, for example, in FIG. 24, so it was necessary to move the image-segment exposure position 17a over long distances along the work 17 with the aid of the actuators 12 and 16 every time the display was switched for an image segment with a large size in the transverse direction. This meant an extended marking time.
A third object of the present invention, which was devised in view of this situation, is to reduce the marking time by selecting an optimum display switching sequence that corresponds to the image size, that is, to the duration of movement in the X and Y directions across the work 17.
Conventionally, as shown in FIG. 26(a), raster scanning such as that shown by the arrow is performed on the display screen 10 of the liquid-crystal mask 6, but the scanning mirror 2 is driven in such a way that a return to a predetermined sub scanning starting position St is effected every time an image segment is switched, and scanning always starts from the starting position St.
It should be noted that the preparation time needed to start such sub scanning is a dead time that produces no actual scanning or marking, and this must be reduced in order to reduce the marking time.
A fourth object of the present invention, which was devised in view of this situation, is to reduce the marking time by reducing the preparation time of sub scanning.
As is also shown in FIGS. 28 and 29, when the object is to mark two images 34 and 35 on the same work 17, the total distance over which the image-segment exposure position 17a is moved by the actuators 12 and 16 across the work 17 sometimes varies depending on whether the display of image segments 19 is alternated between the two images (FIG. 28) or whether the display of the image segments 19 of one of the two images is started after the display of all the image segments 19 of the other one image have been completed (FIG. 29). The result is that movement over long distances across the work 17 is sometimes inevitable when the actuators 12 and 16 are driven in accordance with an unconditionally defined display switching sequence, and this is undesirable if the marking time is to be reduced.
A fifth object of the present invention, which was devised in view of this situation, is to reduce the marking time by selecting an optimum display switching sequence.
Thus, a common object of the present invention is to provide a control device capable of reducing the marking time in a marking device.